Apparatus for making ammonium phosphate.



F- S. WASHBURN. APPARATUS FOR MAKING AMMONIUM PHOSPHATE. APPLICATION FILED APR. 8, m5.

- 1,151 Q74. y Patented Aug. 24, 1915.

Q P Q WWMLM FRANK S. WASHBURN,

0F NASHVILLE, TENNESSEE.

APPARATUS FOR MAKING AMMONIUM PHOSPHATE.

Specification of Letters Patent.

Patented Aug. 24, 1915.

Original application filed August 3, 1914, Serial No. 854,858. Divided and this application filed April 8, 1915. SerialNo.19,966.

To (NW/1on2 it 771 (17 concern Be it known that I, FRANK S. IVASHBURN, a citizen of the United States, residing at Nashville, in the county of Davidson and State of Tennessee, have invented certain new and useful Improvements in Apparatus for Making Ammonium Phosphate; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to an apparatus for making ammonium phosphate especially adapted for fertilizer purposes from phosphate rock, and has for its object to provide an apparatus which will be more etficient and less costly for this purpose than those heretofore proposed.

IVith these and other objects in view the invention consists in the novel details of construction and combinations of parts constituting my invention, all as will be more fully hereinafter disclosed and particularly pointed out in the claims.

This application is a division of my copending application, Serial Number 854,858, filed August 3, 1911, and entitled Process of making mono-ammonium phosphate.

Referring to the accompanying drawing forming a part of this specification in which the figure is a diagrammatic illustration of one form of an apparatus made in accordance with my invention, 1 indicates suitable dissolving-tanks for treating finely divided phosphate rock with sulfuric acid; 2 a filter press for separating the phosphoric acid solution from the insoluble residue; 3 a dis charge pipe from the filter press 2 into the acid heating tank or system (i, and 4 represents any suitable escape pipe for steam from said system.

5 indicates an acid circulating pump connected to the acid heating system 6 as shown, and 11 a pipe for conducting hot acid to the first ammoniating tower 9, while 10 represents a pipe conducting unabsorbed ammonia vapor and gases to a second ammoniating tower 8 connected to the acid heating system 6 by the steam conducting pipe 7.

13 represents an inlet for a mixture of steam and ammonia fed to the first tower 9; and 12 a pipe connecting the acid tank 25 with the adjusting tank 11 adapted to receive super ammoniated acid from tower 9.

understood it is said: I start with finely ground phosphate rock in tank 1, and add sufficient sulfuric acid to the same to convert all of the tri-calcium phosphate into calcium sulfate and free phosphoric acid, and dissolve the impurities in the rock, by adding an additional amount of sulfuric acid. If it is desired to produce this phosphoric acid in a dilute form, the quantity of sulfuric acid to be added need be only sufficient to dissolve the impurities present and convert the tricalcium phosphate into phosphoric acid, but if it is desired to obtain a phosphoric acid in a concentrated solution, containing say as much as 25% P 0 then one must add a slight excess of sulfuric acid in order to take care of the well known chemical phenomena of mass action, which is found to play an increasingly important part in the reaction as the concentration of phosphoric acid in the solutions increases. For instance, if one wishes to obtain a 20% solution of P 0 it is necessary to have in this solution a few tenths of a per cent. of free sulfuric acid in order to obtain a high efficiency of extraction, while if one wishes to work to as high as P 0 in the extracted phosphoric acid, then this solution should contain nearly 1% of free sulfuric acid to obtain high extraction of phosphoric acid from the rock.- I next separate this solution of phosphoric acid from the calcium sulfate and other impurities by filtration as by passing it through the filter press 2, and washing it and I thereby obtain a clear solution of crude phosphoric acid containing only a few tenths of a per cent. of such impurities as iron, alumina and soluble lime, with a slight amount of free sulfuric acid, as above explained.

This said clear solution is led from the filter 2 by means of the pipe 3 to the tank or heating system 6. I may ammoniate this crude solution of phosphoric acid in any suitable manner such as by adding aqua ammonia thereto, or by passing ammonia leaves at the bottom it is transformed into gas into the same. But I prefer to use the ammonia vapor made from commercial calci um cyanamid or lime nitrogen, which contains large quantities ofisteam, at a high temperature. To accomplish this, I fill the towers 8 and 9 with chemical brick, and feed the crude phosphoric acid from the tank into the tower 9 by means of the pipe 11, while the said hot mixture of ammonia and steam as it comes from the cyanamid autoclaves is admitted through the pipe 13. Any unabsorbed gases or vapors in the tower 9 are led from the top thereof to the bottom of tower 8 by means of the pipe 10, while from the top of said tower 8 the pipe 7 leads any unabsorbed gases or vapors into the acid heating system or tank 6 to warm up the acid solution before it reaches tower 9. In

the first tower 9 fed with the ammonia, I so regulate the phosphoric acid that when it a mixture of mono-ammonium and di-ammonium phosphates, with as much of the latter as I can possibly obtain; in other words, in this tower I have a fairly large excess of ammonia. Into the second tower 8, which I use merely as a washing tower for clearing up the ammonia escaped from the first tower, I pass through the pipe 23 a large excess of phosphoric acid, so as to be certain to entrap all the last traces ofammonia. In this way I condense no steam in the system, allow no ammonia to escape unabsorbed, and at the same time make an ammonium phosphate solution quite high in di-ammonium phosphate. This ammonium phosphate solution I then run into the adjusting tank 14, through the pipe 31 and then add sufficient phosphoric acid to exactly neutralize it to the mono-ammonium phos phate stage.

The process of neutralization of this solution I have found involves some complications inasmuch as methyl orange the usual indicator, which has always been used for this work, does not indicate exact neutrality,

butpossesses a lag in its indications; so that if one were to operate without corrections, one would not obtain a strictly neutral solution of mono ammonium phosphate, but would obtain a solution of mono-ammonium phosphate containing about one fourth of 1% of the phosphoric acid in the di-ammonium form. In the subsequent treatment of the product by this process, I have found that di-ammonium phosphateis decomposed into mono-ammonium phosphate, with a consequent loss of ammonia; and, therefore, in order to avoid this loss I find it necessary to correct for this lag of the indicator, by adding a corresponding quantity of phosphoric acid.

I am aware of the fact that there are existing patents callin for the neutralization ofphosphoric acid ldy the use of ammonia,

either in excess or to alkalinity. But such neutralized solutions, if treated in the manner hereinafter described, I have found always lose ammonia, and I, therefore, find it necessary to work in the manner just described, if one desires to avoid such losses.

I have also discovered that such a solution of mono-ammonium phosphate possesses rather peculiar properties in regard to'its temperature concentration phenomena. That is to say, starting with aboiling point of something over 100 0., depending upon the initial concentration of the phosphoric acid, and which for a 20% P 0 solution is approximately 102 C., the boiling point slowly rises with an increase in concentration to, 105 C. From this point on, the rise is much more rapid with an increase of the concentration than it has been up to the said point-until a temperature of 112 C. is reached, at which temperature, if the materialis cooled, it will set to a solid mass, though it is still quite liquid when the temperature of 112 C. is first reached. I therefore conclude that what happens is the following: The rise in temperature from 102 C. up to 105 C. is, probably, simply a concentration of the solution; but from 105 (1., there is probably a true fusion of the separated salt in a saturated solution of ammonium phosphate, up to a temperature of 112 (l, at which point the rest of the water is simply driven off without a rise in temperature. At 112 C. the fused mass contains approximately 10% of water. If

heating is continued this water is lost and the material will set in the evaporating apparatus to a solid mass, which cannot be removed except by a most laborious means. In order to avoid this objection, I evaporate the solution by any suitable means as for example by pumping it from the tank 14: through the pipe 30, into the second effect 16, from which it passes through the pipe 29 to the effect 17, and thence through the pipe 26, pump 18, and pipe 27 into the effect 15. 1 supply the effect 15 with steam through a pipe such as 50 at such a pressure that the temperature of said effect 15 will be substantially' 112 C. I thus obtain in said effect '15 by this system of evaporation a fused product under atmospheric or super atmospheric pressure; and which product I alternately tap out by means of a suitable valve into the highly evacuated receivers 19 and 20. When said product is thus suddenly subjected to the action of a rather high vacuum in the receivers 19 and 20, sensible heat is found to be sufficient to instantly evaporate ofl nearly all the remaining Water, or down to say a content of water of about 3% or 4%, and thesudden expansion of this water is found to puff up the mass into a highly porous condition, somewhat resembling pumice stone, which needs no other drying. This said porous mass is easilygranulated or crushed for admixture with other fertilizers or it can be readily passed through an ordinary drier, without danger of sticking to its walls, and have all of its moisture removed, if desired. By this system of operation I have avoided the very great difficulty of drying a highly concentrated and wet solution of ammonium phosphate, such as would be obtained if ordinary evaporators were used. A product obtained from such ordinary evaporators would be so wet and adhere so strongly to iron that it-would be impossible to dry it through any of the ordinary direct fired types of driers within the limits of reasonable costs.

What I claim is 1. In an apparatus for making monoammonium phosphate from phosphate rock the combination of a tank for holding finely divided rock and sulfuric acid; a filter associated with said tank; a second tank provided with a heating means associated with said filter; an ammoniating tower connected with said second tank; a second ammoniating tower connected with said first named tower; a connection for conducting steam from said second tower to said heating means; and a connection between said second tower and said second tank, substantially as described.

2. In an apparatus for making monoammonium phosphate from phosphate rock the combination of a tank for holding finely divided rock and sulfuric acid; a filter associated with said tank a second tank provided with a heating means associated with said filter; an ammoniating tower connected with said second tank; a second ammoniating tower connected with said first named tower; a connection for conducting steam from said second tower to said heat ing means; a connection between said second tower and said second tank; an adjusting tank associated with said first named tower; a fresh acid tank connected to said adjusting tank; and a pump connected to said second and said last named tanks, substantially as described.

In testimony whereof I aflix my signature.

FRANK S. IVASHBURN. 

